netdev - Re: [PATCH 3/4] rhashtable: use bit_spin

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Message-ID: <20190327034543.aiskjamfllevxigg@gondor.apana.org.au>
Date:   Wed, 27 Mar 2019 11:45:44 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     NeilBrown <neilb@...e.com>
Cc:     Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: Re: [PATCH 3/4] rhashtable: use bit_spin_locks to protect hash
 bucket.

On Wed, Mar 27, 2019 at 09:35:18AM +1100, NeilBrown wrote:
> 
> The bit_spin_unlock(), which I am avoiding as unnecessary, would have
> provided release semantics.
> i.e. any write by this CPU that happened before the releasing write
> will be visible to other CPUs before (or when) they see the result of
> the releasing write.
> This is (as I understand it) exactly that rcu_assign_pointer() promises
> - even before acquire semantics were added as Paul just reported.
> 
> So yes, I am sure (surer now that I've walked through it carefully).

Given that rcu_assign_pointer now does a store release it should
indeed be safe.  Thanks!
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt